I think that was one of the D&G meets that I showed for. I remember talking to the owner briefly and him saying that those were formed by cutting slices into the fender and pulling them out, and then welding new metal in and refinishing.

Those are awesome! That guy is either the best metal man on the planet or there is a ton of bondo on there.
From my personal experience, one would have to slice the fender upwards from the arch to get that much strectch out of the fender.

The flares are approximately 2" wider in the back, and about 1-1/2" wider in the front. What will fit depends on wheel back-spacing, ride height, suspension stiffness, and tire size. Too many variables to be accurate about what tire will fit. There is some discretion on the part of the installer as to how wide the flares end up. For more on this perform a search for flares. The link below has some pictures.